Catherine Drennan

The Drennan laboratory uses X-ray crystallography as the chief tool for investigating the structure and function of enzymes that are medically important or valuable in environmental remediation. We are particularly interested in metalloprotein biochemistry and in the role of conformational change in catalysis.

The Drennan laboratory seeks to understand how Nature harnesses and re-directs the reactivity of enzyme metallocenters in order to perform challenging reactions. By combining X-ray crystallography with other biophysical methods, our goal is to “visualize” molecular processes by obtaining snapshots of enzymes in action.

Why snapshots? Suppose one wants to understand the process by which a mechanic changes the battery in your car. One photo of a mechanic standing by the car won’t do the trick, but a series of photos of the mechanic changing the battery would be most informative. The same is true when one wants to understand a cellular process; one image of a key enzyme only tells you so much. Thus our laboratory employs multiple biophysical methods to aid in the “visualization” of complex enzyme processes.

Of what do we take snapshots? We want to understand how nature performs the most challenging reactions. Often difficult reactions require the use of organic cofactors or metal ions, which enhance enzyme reactivity. Thus metallo- and cofactor-dependent enzymes are our primary targets. A case in point is the reaction of class I ribonucleotide reductase (RNR), which utilizes a di-iron cofactor to generate protein-based radical species, essential for the reduction of ribonucleotides to deoxyribonucleotides. Although enzymatic reactions like that of RNR are simply spectacular, structural characterization of these enzymes is non-trivial due to issues such as conformational flexibility, protein heterogeneity, structural complexity, and oxygen sensitivity. Our laboratory has specialized in tackling and solving these more challenging structural biology problems. In addition to our focus on radical-based enzymology, we also study metallo- and cofactor-containing enzymes involved in carbon dioxide sequestration and methylation chemistry. Here we seek to obtain snapshots to understand how one-carbon units such as CO2 or CH3 are transferred from enzyme to enzyme, either as part of microbial CO2 fixation pathways or as part of methylation chemistry in humans. In addition, we are interested in how metallocofactors are assembled on their target enzyme and in the regulation of metal uptake by cells.

How do we take snapshots? Although our main technique is X-ray crystallography, we have recently expanded our toolbox and we now combine crystallographic results with data from a variety of other methods, including small angle X-ray scattering (SAXS), electron microscopy (EM), analytical ultracentrifugation (AUC), computational biophysics, absorbance spectroscopy and nuclear magnetic resonance (NMR). Hypotheses generated from our structures can then be tested using both in vitro and in vivo methods.